A) Field of the Invention
The present invention relates to a semiconductor storage device, and more particularly to a semiconductor storage device having signal wiring lines formed above the region where memory cells are disposed.
B) Description of the Related Art
If signal wiring lines and the like are disposed above bit lines applied to which are signals read from memory cells of a semiconductor storage device, electric signals transmitted in the signal wiring lines generate noises in the bit lines. In order to prevent the generation of noises, signal wiring lines and the like have been conventionally designed not to be disposed above the memory cell region.
As the memory cell region becomes large because of a large capacity of a semiconductor storage device, an area where signal wiring lines cannot be disposed becomes broad. It is therefore necessary to enlarge the chip area or increase the number of wiring layers in order to allow necessary signal wiring lines to be disposed in an area other than the memory cell region.
Even if signal wiring lines are disposed above bit lines, the generation of noises in the bit lines can be prevented if a shield layer is disposed between the bit lines and signal wiring lines.
A conductive shield layer and an interlayer insulating film have different thermal expansion coefficients. Since the shield layer covers a broader area than other wiring patterns, a large stress is applied to the edge of the shield layer, resulting in a lower manufacture yield.